The ellipsometric technique is a powerful multi-functional light division technology, used to obtain characteristics information about target surfaces by detecting electromagnetic waves. The characteristics information may include reflectivity, thickness, refractive index, extinction parameters, polarization, surface microstructure, particles, defects, and roughness of the target surface or the thin film surface, and so on. Because the ellipsometric technique is a highly sensitive, non-destructive, and no-contact measurement technique, it is widely used in a variety of fields from basic research to industrial applications, including semiconductor physics, microelectronics, and various areas of biology.
Existing ellipsometric measurement technology works as follows: A light source emits light which passes through a first polarizing plate (often called the polarizer) to generate a polarized light. Then the polarized light illuminates a target surface. The polarized light changes its polarization state after interacting with the target surface. The light then passes through a second polarizer (often called the analyzer), and then enters a detecting device. The ellipsometric technology analyzes light intensity, phase, and polarization states of the light reflected by the target samples, and accordingly obtains the characteristics information that is detected by the electromagnetic waves as they interact with the target surface. This technique works even if the thickness of the target is shorter than the wavelength of the detecting light, e.g., a thickness that is equal or even less than a single atomic layer.
In general, ellipsometry is a technique based on light mirror reflection, in which the incident angle is equal to the reflection azimuthal angle, and the incident light path and the reflected light path are in the same plane (called the incident plane). In the text to follow, the components of the electric field of the polarized light that are parallel with and perpendicular to this incident plane are respectively defined as “p” and “s” components of the polarized light. The polarization state of the polarized light upon interaction with the target surface can change due to various mechanisms, including reflection, transmission, diffraction, and so on. In this application, without loss of generality, the main conditions for reflection are introduced. Because in existing ellipsometry techniques, each measurement can only obtain one set of experimental data, these techniques generally use a rotating ellipsometry method. According to this method, a first motor rotates the polarizer to change the polarizer's azimuthal angle. Similarly, a second motor rotates the second polarizer (the analyzer) to change the analyzer azimuthal angle. Based on all the polarizer azimuthal angles, a set of data can be obtained, and accordingly the characteristics of the target surface can be determined. Therefore, since the existing techniques require a set of data, these techniques suffer some shortcomings, such as long data measuring time, method complexity, and expensive hardware.